Apparatus and method for detecting co-channels signals

ABSTRACT

Apparatus and method for recognizing Global System for Mobile communication (GSM) signals are provided. The solution comprises obtaining position and timing information from a satellite positioning system; tuning to a frequency channel with GSM transmission; collecting a group of I/Q samples for the length of 12 GSM frames; performing peak detection using at least two peak detectors over the group of samples wherein the found peak values are the locations of synchronization bursts (SCH). For the found peaks, the timing information, carrier-to-noise ratio, in phase and quadrature values are determined. A group of I/Q samples for the length of 12 or 51 GSM frames are collected. From the found SCH, base station identification code BSIC, frame number and Broadcast Control Channel (BCCH) training sequence are determined. BCCHs corresponding to all SCH are decoded; and transmitting base stations identified.

FIELD

The exemplary and non-limiting embodiments of the invention relategenerally to an apparatus and a method in wireless communicationnetworks. Embodiments of the invention relate especially to detectingco-channel signals in wireless communication environment.

BACKGROUND

The following description of background art may include insights,discoveries, understandings or disclosures, or associations togetherwith disclosures not known to the relevant art prior to the presentinvention but provided by the invention. Some of such contributions ofthe invention may be specifically pointed out below, whereas other suchcontributions of the invention will be apparent from their context.

Because frequency spectrum is a limited resource, several communicationsystems may share the same spectrum. In a given frequency spectrum agiven number of frequency bands may be given to different operators orcarriers in different locations. Typically each operator performsindependent cellular coverage planning.

Present day methods for measuring cellular coverage in a cellularcarrier's networks utilize radio scanners which operate in the cellularfrequency bands. Typically, a route is driven using a vehicle equippedwith the scanner equipment for collecting over-the-air downlink signalsfrom the carrier's cell sites. GPS is used to geographically map thecoverage area using specific signaling parameters for a given cellulartechnology. For Global System for Mobile communication (GSM) systems,signaling parameters measured and collected include received signalstrength (RSSI), carrier-to-noise plus interference (CINR), the basestation identifier code (BSIC), and broadcast channel (BCCH) messages.Within the BCCH messages are radio resource pseudo-length messages asspecified in 3GPP standards. Within the set of BCCH messages includeSystem Info Type 3 and 4 messages which provide information detailingthe specific cell id, country code (MCC), network code (MNC), andlocation area code (LAC), among other information.

Present-day equipment offers the ability to show BSIC values and CINRvalues along with the GPS mapping of the carrier's coverage area whichhelp reveal where there might be co-channel problems. Co-channelinterference occurs when the frequency reuse plans are not optimized ina cellular network. In other words, two cell sites which cover the sameregion occupy the exact same radio frequency (the same absoluteradio-frequency channel number, ARFCN). Typically a network isconsidered optimized if the CINR is maintained around 8-9 dB with RSSIlevels down to −102 dB at which point a cellular phone would perform ahand-off to another stronger cell and is designed to operate.

However, present-day scanners do not provide simultaneous collection ofmore than one base station signal. Thus, both the desired and theinterfering signals cannot be decoded simultaneously. Typically the onlyway of detecting possible co-channel interference is finding that themeasured CINR is below the expected 8-9 dB with received signal strengthabove −102 dB. The existence and identification of co-channelinterference is possible only when the collected data is post-processedin laboratory environment. This is tedious and slow.

SUMMARY

The following presents a simplified summary of the invention in order toprovide a basic understanding of some aspects of the invention. Thissummary is not an extensive overview of the invention. It is notintended to identify key/critical elements of the invention or todelineate the scope of the invention. Its sole purpose is to presentsome concepts of the invention in a simplified form as a prelude to amore detailed description that is presented later.

According to an aspect of the present invention, there is provided anapparatus comprising at least one processor configured to cause theapparatus to: control a satellite positioning system receiver to obtainposition and timing information from a satellite positioning system;control a receiver to tune to a frequency channel with Global System forMobile communication (GSM) transmission; control a receiver to collect agroup of in phase and quadrature (I/Q) samples for the length of 12 GSMframes; perform correlation on the group of I and Q samples; performpeak detection using at least two peak detectors over the group ofsamples wherein the found peak values are the locations ofsynchronization bursts (SCH); for the found peaks, determine the timinginformation, carrier-to-noise ratio, in phase and quadrature values;control a receiver to collect a group of in phase and quadrature (I/Q)samples for the length of 12 or 51 GSM frames; from the found SCH,determine base station identification code BSIC, frame number andBroadcast Control Channel (BCCH) training sequence for all SCH; decodeBCCHs corresponding to all SCH; and determine time-difference-of-arrival(TDOA) between the found peak values using the determined timinginformation.

According to another aspect of the present invention, there is providedA method for recognizing Global System for Mobile communication (GSM)signals, the method comprising: obtaining position and timinginformation from a satellite positioning system; tuning to a frequencychannel with Global System for Mobile communication (GSM) transmission;collecting a group of in phase and quadrature (I/Q) samples for thelength of 12 GSM frames; performing correlation on the group of I and Qsamples; performing peak detection using at least two peak detectorsover the group of samples wherein the found peak values are thelocations of synchronization bursts (SCH); for the found peaks,determining the timing information, carrier-to-noise ratio, in phase andquadrature values; collecting a group of in phase and quadrature (UQ)samples for the length of 12 or 51 GSM frames; from the found SCH,determining base station identification code BSIC, frame number andBroadcast Control Channel (BCCH) training sequence for all SCH; decodingBCCHs corresponding to all SCH; and determining time-difference-ofarrival (TDOA) between the found peak values using the determined timinginformation.

LIST OF DRAWINGS

Embodiments of the present invention are described below, by way ofexample only, with reference to the accompanying drawings, in which

FIG. 1 illustrates an example of a communication environment;

FIG. 2 illustrates an example of a GSM frame structure;

FIG. 3 illustrates the structure of the GSM synchronization burst

FIGS. 4A and 4B are flowcharts illustrating examples of embodiments ofthe invention;

FIG. 5 illustrates an example of correlation results; and

FIG. 6 illustrates an example of an apparatus.

DESCRIPTION OF SOME EMBODIMENTS

Embodiments are applicable to any base station, user equipment (UE),server, corresponding component, and/or to any communication system orany combination of different communication systems that support requiredfunctionalities.

The protocols used, the specifications of communication systems, serversand user terminals, especially in wireless communication, developrapidly. Such development may require extra changes to an embodiment.Therefore, all words and expressions should be interpreted broadly andthey are intended to illustrate, not to restrict, embodiments.

Many different radio protocols to be used in communications systemsexist. Some examples of different communication systems are theuniversal mobile telecommunications system (UMTS) radio access network(UTRAN or E-UTRAN), long term evolution (LTE, known also as E-UTRA),long term evolution advanced (LTE-A), Wireless Local Area Network (WLAN)based on IEEE 802.11 stardard, worldwide interoperability for microwaveaccess (WiMAX), personal communications services (PCS) and systems usingultra-wideband (UWB) technology. IEEE refers to the Institute ofElectrical and Electronics Engineers.

FIG. 1 illustrates a simplified view of a communication environment onlyshowing some elements and functional entities, all being logical unitswhose implementation may differ from what is shown. The connectionsshown in FIG. 1 are logical connections; the actual physical connectionsmay be different. It is apparent to a person skilled in the art that thesystems also comprise other functions and structures. It should beappreciated that the functions, structures, elements and the protocolsused in or for communication are irrelevant to the actual invention.Therefore, they need not to be discussed in more detail here.

FIG. 1 shows an apparatus 100 traveling 102 in an area which is servedby more than one two base stations 104, 106 of a communication system110. The base stations have coverage areas 112, 114 where thetransmissions of the base stations are well received.

The apparatus 100 configured to receive the transmissions of the basestations. In this particular example, the apparatus 100 is so situatedthat it may receive the transmission 118 from base station 104 and thetransmission 120 from base station 106. It should be noted thatembodiments of the invention are not limited to any particular number ofbase stations.

The apparatus may be a scanner configured to measure and analyze thecellular coverage of a network or a system. Let assume that in theexample of FIG. 1 the apparatus is configured to measure the cellularcoverage of system 110. The apparatus may also be user equipmentconfigured by the system to perform measurements along with normaloperation. The apparatus may be user equipment, mobile station, a fixedstation, a portable or fixed communication apparatus, a measurement oranalyzing device, a scanner or any other kind of device configured toreceive transmissions from base stations of communication systems. Theapparatus may be a standalone device or it may be connectable to otherdevices such as personal computers, analyzers or other devices.

In an embodiment, the apparatus 100 is a software defined radio SDR. InSDR, many components traditionally implemented with hardware arerealized as software running in one or more processors.

In this example, the communication system 110 is a GSM based systems andthe base stations 104, 106 GSM base stations In GSM based systems, thebase stations transmit a base station identification code BSIC whichidentifies the base station. Transceivers wishing to communicate withbase stations detect the BSIC of the base stations before initiatingcommunication with the base stations. As already mentioned, each basestation transmits broadcast channel (BCCH) messages. The BCCH messagesare provide information detailing the specific cell id, country code(MCC), network code (MNC), and location area code (LAC), among otherinformation.

In usual circumstances, the frequencies allocated to nearby basestations do not overlap. However, there may be situations when the cellplanning of different network carrier operators is not optimal andnearby cells use the same frequency. In the example of FIG. 1 let usassume that both base stations 104, 106 transmit on the same frequencychannel. Thus, when the apparatus 100 measures the cell coverage of basestation 104 it may receive the transmission of base station 106 asco-channel interference.

The interfering base stations need not be geographically adjacent. Ifthe frequency reuse plan of a network is not optimal the signal of abase station farther away may extend farther as originally intended andcause interference to the operation of another base station of the samenetwork carrier.

As with most cellular communication systems, GSM transmission includestraffic channels and signaling channels. The signaling channels includethe following:

Broadcast Channels (BCH)

Broadcast Control Channel (BCCH)

Frequency Correction Channel (FCCH)

Synchronization Channel (SCH)

Cell Broadcast Channel (CBCH)

Common Control Channels (CCCH)

Paging Channel (PCH)

Random Access Channel (RACH)

Access Grant Channel (AGCH)

Standalone Dedicated Control Channel (SDCCH)

Associated Control Channel (ACCH)

Fast Associated Control Channel (FACCH)

Slow Associated Control Channel (SACCH)

When a conventional GSM transceiver or receiver, whether being userequipment or a scanner, is turned on or arrives to a new geographicalarea it is configured to search for Frequency Correction Channel FCCHtransmitted by all base stations. When FCCH is found the transceiverknows where Synchronization Channel SCH is located. From SCH thetransceiver gets BSIC, BCC and information needed to receive BroadcastControl Channel BCCH and identify the base station and connect to thebase station if needed.

A typical GSM network signaling uses a repeating multi-frame sequence oftwo 51-frame multi-frames to include the SACCH channels. An example ofthis structure is illustrated in FIG. 2. Figure shows two successivemulti-frames 200, 202 of a typical downlink channel in a GSM network.Here the repeating SCH bursts are to be noted as it is useful for theidentification of co-channel signals. These bursts occur every 11 frameson the forward or downlink control channel. It should be noted that anyperiodic synchronization signaling within the 51 frame multi-frame couldbe used including the training sequences for normal bursts in additionto the extended training sequence in the SCH bursts. The advantage ofthe SCH bursts is the high repetition rate and the significance of 64training sequence bits vs the 26 bits used for normal bursts.

The Slow Associated Control Channel SACCH that is associated with eachStandalone Dedicated Control Channel SDCCH is only transmitted everyother multi-frame. Each SACCH only gets half of the transmit time as theSDCCH that it is associated with. So, in one multi-frame, SACCH0 andSACCH1 would be transmitted, and in the next multi-frame, SACCH2 andSACCH3 would be transmitted.

FIG. 3 illustrates the structure of the GSM synchronization burst SCH.The purpose of the SCH burst is to provide synchronization for themobiles on the network. In the beginning of the burst are three tailbits which at the start of the GSM burst give time for a transmitter toramp up its power. Then follow 39 bits of information, 64 bits of a Longor Extended Training Sequence and another 39 bits of Information.Finally, three 3 tail bits to enable the transmitter power to ramp downand 8.25 bits guard time to act as a guard interval.

A SCH burst contains a 64 bit extended training sequence which canprovide a strong correlation gain even for weak signals. Typical GSMphones are designed to operate with a received signal having a signallevel below −102 dBm. In a network the GSM performance should be capableof maintaining an 8 or 9 dB carrier-to-noise and interference (CINR)level for optimum performance to minimize bit errors. When two or moreGSM signals operate on the same RF channel or ARFCN co-channelinterference results. By using the SCH bursts as an indicator ofco-channel signals the relative timing between the transmitters ortime-difference-of-arrival (TDOA) of the signals and actual cellidentification using BSIC decoding and/or broadcast channel (BCCH)decoding can identify the cells which are transmitting on the samefrequency. Then the network operator, knowing the cells and GPScoordinates, can remedy the situation by changing the operatingfrequencies and/or the network frequency reuse plan. The networkoperator may utilize a movable scanner collecting and logging results inconjunction with GPS location(s) where the co-channel was detected.

FIGS. 4A and 4B illustrate embodiments of the invention. The embodimentsdiffer in the number of samples acquired. In the embodiment of FIG. 4Asamples for the length of 12 GSM frames are collected whereas in theembodiment of FIG. 4B samples for the length of 51 GSM frames arecollected. The selection whether to collect samples for the duration oflength of 12 or 51 GSM frames is an implementation issue and dependsupon application. If speed is of concern, the 12 frames may becollected. However, when 51 frames are collected it is guaranteed thatthe BCCH 4 frame bursts would be collected.

In the 12 frame configuration for collection the probability ofcollecting the BCCH 4 frame bursts is not as good as in the 51 frameconfiguration but the speed at which the process may be done is overfour times faster. Thus, when 12 frames are collected BSIC decoding maybe performed accurately. The selection of the frame configuration isused to help optimize scanning performance depending on whether one isinterested in scanning a lot of channels (use the 12 frameconfiguration) or one is interested in scanning a few channels where theuser could use the 51 frame configuration. The 51 frame configurationmay be used to ensure the collect of the BCCH messages which are radioresource messages and specifically to be able to decode the System InfoType 3 and 4 messages which include cell identification information.

FIG. 4A is a flowchart illustrating an embodiment of the operation ofthe apparatus 100 of FIG. 1.

The embodiment starts at step 400.

In step 402, position and absolute timing information is obtained from asatellite positioning system. This may be done by controlling a GPSreceiver to obtain required information. Absolute timing informationmeans in this context the time kept by the GPS.

In step 404, the receiver or transceiver of the apparatus is tuned to afrequency channel with GSM transmission. Thus, the receiver ortransceiver searches for FCCH signal transmitted by a base station andwhen found, tunes to the found channel. FCCH is used for the purpose offinding a channel because in GSM system it is specifically designed forthis purpose.

In step 406, the receiver or transceiver of the apparatus collects agroup of in phase and quadrature (I/Q) samples for the length of 12 GSMframes. In an embodiment, the receiver or transceiver performs GSM SCHmatched filtering of I and Q signal paths over 12 complete GSM frameperiods at a sample rate of 2× symbol rate resulting over 2500 samples.

In step 407, correlation is performed on the group of I and Q samples.In an embodiment, the correlation is performed using afield-programmable gate array (FPGA). In an embodiment, the correlationis implemented using 114 tap filter for each I and Q channel. At adouble sample rate of the symbol rate for non-GMSK modulation 128 tapsmay be useful. For GSMK the modulation necessary to generate the I and Qcoefficients renders some symbols ineffective due to the forward lookingeffect in GMSK modulation. In an embodiment, four forward lookingsymbols are used. Thus, out of 64 symbols the first three and the lastthree are not represented providing symbols 4-61 or 57 useful symbols.

For GMSK, each symbol is a composite of preceding symbols so the firstthree and the last three symbols of the 64 symbol long training sequenceare indeterminant. The 114 tap length correlation then accounts for atbest 57 of the 64 symbols. In an embodiment, the symbols at the frontand at the end are skipped during the tap 114 I and Q channelcorrelation process.

In step 408, peak detection is performed using at least two peakdetectors over the group of samples wherein the found peak values arethe locations of synchronization bursts (SCH). In an embodiment, theapparatus performs peak detection of SCH matched filter normalizedmagnitude over collect of 12 frame sample data to encompass one completetransmittal of FCCH+SCH bursts repetition interval.

In a typical case two peak detectors are utilized. In such a caseprimary and one secondary or co-channel signal may be detected andrecognized. This covers the majority of cases as it would be rare tohave three nearby GSM base stations utilize the same frequency channel.

In step 410, for the found peaks, timing information, carrier-to-noiseratio and in phase and quadrature values are determined. In anembodiment, the determination of timing information comprises timestamping peak positions as an index offset relative to a GPS 1 PPS (1Pulse per Second signal aligned to Coordinated Universal Time UTC) andto each other.

In an embodiment, parameters determined for each significant SCH burstpeak detected include for example following:

The sample index relative to the start of the sample of collect may bedetermined and the sample index relative to GPS time offset from 1 sec.Normalized correlation peak or signal to noise ratio, Es²/Io²(n), wheren is the index of the sample with the peak value is calculated. Inaddition, normalized correlation peak one sample early, Es²/Io²(n−1) andnormalized correlation peak one sample later, Es²/Io²(n+1) may bedetermined, where n is the index of the sample with the peak value iscalculated. The Es2/Io2 values may be used to obtain a more refinedtiming estimate for timing adjustments in the demodulation and decodingof the SCH bursts. The three peak values at n, n−1, and n+1 may be usedin a parabolic fit algorithm to estimate the fractional timing errorbased on the proportion of the correlation in the adjacent samples. A−0.5 to +0.5 timing adjustment can be made to locate the optimumfractional resampling point for demodulation and decoding.

Furthermore, in phase and quadrature (I and Q) values may be determinedfor samples of the correlation peaks, I and Q values at one sample laterand at one sample early of correlation peaks and also Io², average ofsamples.

The computation of CINR using Es²/Io² for both primary and secondary orco-channel signals provides valuable and useful information. The CINRnoise floor with no co-channel should typically be around −6 dB. When aco-channel interference signal exists, the primary CINR may decreasebelow the preferred 8/9 dB.

An example of an equation which may be used to compute carrier-to-noiseand interference (CINR) using the parabolic fitted Es²/Io² value is:CINR=10*log(Es ²/(Io ² −Es ²)).

In step 412, the apparatus is configured to determinetime-difference-of-arrival (TDOA) between the found peak values usingthe determined timing information. The apparatus may be configured tocalculate the timing or time-difference-of-arrival (TDOA) between twodominant and significant peaks using the SCH burst correlation indexes.

In step 414, the apparatus is configured to, from the both dominant SCHsfound, determine base station identification code BSIC.

The process ends in step 416.

FIG. 4B is a flowchart illustrating another embodiment of the operationof the apparatus 100 of FIG. 1.

The embodiment starts at step 420.

The step 422 is similar to the step 402 of FIG. 4A, i.e., position andabsolute timing information is obtained from a satellite positioningsystem.

The step 424 is similar to the step 404 of FIG. 4A, i.e., the receiveror transceiver of the apparatus is tuned to a frequency channel with GSMtransmission.

In step 426, the receiver or transceiver of the apparatus collects agroup of in phase and quadrature (I/Q) samples for the length of 51 GSMframes.

In step 427, correlation is performed on the group of I and Q samples ina similar manner as described in connection with step 407 above. In anembodiment, the correlation is performed using a field-programmable gatearray (FPGA).

In step 428, peak detection is performed using at least two peakdetectors over the group of samples. Further, in step 430, for the foundpeaks, timing information, carrier-to-noise ratio and in phase andquadrature values are determined. In processing the 51 frame collectionof a GSM signal the SCH bursts of both primary and co-channel signalswill be contained in the collect. This is due to the fact that all GSMdownlink signaling will repeat at the 51 frame multi-frame sequence andthe SCH bursts will repeat every 10 or 11 frames. The SCH matchedfilter/correlator will provide correlation peaks at the SCH burstlocations of the two signals. FIG. 5 illustrates an example ofcorrelation results with the primary and co-channel signal peaks. Inthis example, a first GSM signal is a few dB below the other GSM signal.In the example of FIG. 5, the correlation result for odd samples isillustrated, with the sample number on the x-axis and the correlation ony-axis. Here the two dominant peaks occur, one 500 just above the samplenumber 2000 and another 502 just below the sample number 12000.

By acquiring the sample indexes of the peak values the apparatus isagile and can quickly locate the SCH burst samples collected and decodethe BSIC and/or the BCCH bursts if they also are contained in thecollect. The BCCH bursts are included if the SCH burst either occurredsufficiently early in the collect or sufficiently later in the collect.

In step 432, the apparatus is configured to determinetime-difference-of-arrival (TDOA) between the found peak values usingthe determined timing information.

In step 434, the apparatus is configured to, from the both dominant SCHsfound, determine base station identification code BSIC, the number ofthe frame where the SCH is and Broadcast Control Channel (BCCH) trainingsequence for the found SCHs. On the basis of the frame number theapparatus is able to find the BCCH.

In step 436, the apparatus is configured to decode BCCHs correspondingto the found SCHs. The apparatus is configured to perform BCCH burstprocessing of both dominant SCH burst peaks to decode System Info Type 3and 4 radio resource messages which include cell id and cell siteinformation included in System Info Type 3 and 4.

In an embodiment, the apparatus is configured to associate decoded SCHand BCCH bursts with the received primary and co-channel signals toidentify interfering cells.

The process ends in step 438.

Since separate cell sites are not necessarily frame aligned the SCH andBCCH bursts from one cell site most likely will occur in a differenttime position over the 10/11 GSM frame periods than the SCH and BCCHbursts from another cell site when both are transmitting on the sameARFCN.

The ability to GPS time stamp the peak locations is utilized intime-difference-of-arrival (TDOA) measurements. When the either theCINRs of the two interfering cells are too weak to decode any of the SCHor BCCH bursts without errors the synchronization signals (SCH bursts)will remain dominant and the CINRs and TDOAs will be valuableinformation for associating the two and tracking the interferencepatterns during a drive of the network.

When the BSICs and BCCH bursts can be decoded then the information canbe completed to associate the cells exactly. In cases where the networkoperator knows the cell site database information the BSICs alone may besufficient information. Also, the BCCH bursts being decoded andspecifically the System Info Type 3 message contents can be used toexactly identify the cells in an operator's network.

In developing the present solution it was discovered that a good way tovisualize the co-channel environment would be to identify and associatetiming information with the occasional decodes of the GSM BSIC and/orBCCH of the signals. This way the two interfering GSM signals can beproperly identified over time. When an interfering signal such asco-channel exists the direct signal as well as the co-channel signal mayboth be difficult to decode successfully without cyclic redundancy check(CRC) errors. At some point during a test drive both signals may be ableto be successfully decoded due to the time varying propagationconditions. Although they may not both be successfully decoded at thesame time the timing relationship can be associated when they aredecoded.

A signal's frame number and timing is provided by the GSM frame numberwhen a successful BSIC decode occurs with the addition of a timing indexrelative to GPS from the scanning hardware. The timing index is directlyrelated to the GSM SCH burst within a GSM frame. When the signals can bedecoded without CRC errors they can be tagged and associated with thetiming information. The GSM SCH correlations present significant peakswhich are used to establish timing indexes relative to GPS. If these areplotted over time the interference patterns will be clearly revealed.The GSM signal will most likely have CRC errors when co-channel ispresent. Although there are CRC errors the fact that the status showsCRC errors coupled with a CINR near 0 dB implies the presence of asignificant SCH burst and decode attempt. The presence of multiple GSMSCH bursts will still provide timing indexes that can be plotted. Oncethe SCH burst can be decoded to extract the BSICs then the associationto the timing information can be established. Over time both direct andco-channel signals will be decoded.

Whether a BSIC or BCCH decode is successful or not the SCH burst timingand TDOA may be provided along with the measured CINR. As describedpreviously eventually successful decodes will occur. For GSM signalswhen there are significant CRC errors in the BSIC decoding operationthere most likely exists co-channel interference, multipathinterference, or weak signal conditions. Utilization of the time indexesand Es/Io (CINR) values for the two dominant peaks will reveal thepresence of the interference. Eventually each of the two signals will besuccessfully decoded and reveal itself in terms of BSIC code, framenumber, and BCCH information. The GPS mapping will also provide theoperator locations of specific interference problems.

FIG. 6 illustrates an embodiment. The figure illustrates a simplifiedexample of an apparatus 100 applying embodiments of the invention. Insome embodiments, the apparatus may be user equipment of acommunications system. The apparatus may further be a measurement oranalyzing device, a scanner or any other kind of device configured toreceive transmissions from base stations or other elements ofcommunication systems. The apparatus may be a standalone device or itmay be connectable to other devices such as personal computers,analyzers or other devices.

The apparatus may also be interpreted as a circuitry implementing therequired functionality within user equipment of a communications systemor a measuring or analyzing device.

It should be understood that the apparatus is depicted herein as anexample illustrating some embodiments. It is apparent to a personskilled in the art that the apparatus may also comprise other functionsand/or structures and not all described functions and structures arerequired. Although the apparatus has been depicted as one entity,different modules and memory may be implemented in one or more physicalor logical entities.

The apparatus of the example includes a control circuitry 600 configuredto control at least part of the operation of the apparatus.

The apparatus may comprise a memory 602 for storing data. Furthermorethe memory may store software 604 executable by the control circuitry600. The memory may be integrated in the control circuitry.

The apparatus comprises a transceiver 606. The transceiver isoperationally connected to the control circuitry 600. It may beconnected to an antenna arrangement 608.

The software 604 may comprise a computer program comprising program codemeans adapted to cause the control circuitry 600 of the apparatus tocontrol the apparatus to control a satellite positioning system receiverto obtain position and timing information from a satellite positioningsystem; control a receiver to tune to a frequency channel with GlobalSystem for Mobile communication (GSM) transmission; control a receiverto collect a group of in phase and quadrature (I/Q) samples for thelength of 12 GSM frames; perform peak detection using at least two peakdetectors over the group of samples wherein the found peak values arethe locations of synchronization bursts (SCH); for the found peaks,determine the timing information, carrier-to-noise ratio, in phase andquadrature values; control a receiver to collect a group of in phase andquadrature (I/Q) samples for the length of 12 or 51 GSM frames; from thefound SCH, determine base station identification code BSIC, frame numberand Broadcast Control Channel (BCCH) training sequence for all SCH;decode BCCHs corresponding to all SCH; and determinetime-difference-of-arrival (TDOA) between the found peak values usingthe determined timing information.

The apparatus may further comprise interface circuitry 610 configured toconnect the apparatus to other devices and network elements ofcommunication system The interface may provide a wired or wirelessconnection to personal computers, analyzers or other devices.

The apparatus may further comprise user interface 610 operationallyconnected to the control circuitry 600. The user interface may comprisea display, a keyboard or keypad, a microphone and a speaker, forexample.

The apparatus may further comprise a satellite positioning receiver 612such as a Global Positioning System (GPS) receiver operationallyconnected to the control circuitry 600.

In an embodiment, a matched filter used to detect SCH is implemented ina field-programmable gate array (FPGA) and operates on both the in phaseand quadrature samples at a double sample rate or 270833 samples/sec×2.Higher sample rate filters are feasible for higher number of samples persymbol. In this implementation two samples per symbol were used.

The FPGA may also comprise two peak detectors, a primary and a secondarydetector, which operate in tandem to minimize duplication of obtainingthe same peaks.

In an embodiment, a traditional peak detector which operates over the 12frames of the collected data may be used. The second peak detector isslaved to the first peak detector with limitations to prevent capturingthe same peaks.

When the primary peak detector updates the secondary peak detector isdisabled. The transfer of the primary peak to the secondary peakdetector can occur only if not outside a window of the previous primarypeak index. Also, the secondary peak update will not update when a peakis detected within a few samples of the primary index+10 frames. Thiswill prevent capture of the same repeating SCH burst peak.

The steps and related functions described in the above and attachedfigures are in no absolute chronological order, and some of the stepsmay be performed simultaneously or in an order differing from the givenone. Other functions can also be executed between the steps or withinthe steps. Some of the steps can also be left out or replaced with acorresponding step.

The apparatuses or controllers able to perform the above-described stepsmay be implemented as an electronic digital computer, which may comprisea working memory (RAM), a central processing unit (CPU), and a systemclock. The CPU may comprise a set of registers, an arithmetic logicunit, and a controller. The controller is controlled by a sequence ofprogram instructions transferred to the CPU from the RAM. The controllermay contain a number of microinstructions for basic operations. Theimplementation of microinstructions may vary depending on the CPUdesign. The program instructions may be coded by a programming language,which may be a high-level programming language, such as C, Java, etc.,or a low-level programming language, such as a machine language, or anassembler. The electronic digital computer may also have an operatingsystem, which may provide system services to a computer program writtenwith the program instructions.

As used in this application, the term ‘circuitry’ refers to all of thefollowing: (a) hardware-only circuit implementations, such asimplementations in only analog and/or digital circuitry, and (b)combinations of circuits and software (and/or firmware), such as (asapplicable): (i) a combination of processor(s) or (ii) portions ofprocessor(s)/software including digital signal processor(s), software,and memory(ies) that work together to cause an apparatus to performvarious functions, and (c) circuits, such as a microprocessor(s) or aportion of a microprocessor(s), that require software or firmware foroperation, even if the software or firmware is not physically present.

This definition of ‘circuitry’ applies to all uses of this term in thisapplication. As a further example, as used in this application, the term‘circuitry’ would also cover an implementation of merely a processor (ormultiple processors) or a portion of a processor and its (or their)accompanying software and/or firmware. The term ‘circuitry’ would alsocover, for example and if applicable to the particular element, abaseband integrated circuit or applications processor integrated circuitfor a mobile phone or a similar integrated circuit in a server, acellular network device, or another network device.

An embodiment provides a computer program embodied on a distributionmedium, comprising program instructions which, when loaded into anelectronic apparatus, are configured to control the apparatus to executethe embodiments described above.

The computer program may be in source code form, object code form, or insome intermediate form, and it may be stored in some sort of carrier,which may be any entity or device capable of carrying the program. Suchcarriers include a record medium, computer memory, read-only memory, anda software distribution package, for example. Depending on theprocessing power needed, the computer program may be executed in asingle electronic digital computer or it may be distributed amongst anumber of computers.

The apparatus may also be implemented as one or more integratedcircuits, such as application-specific integrated circuits ASIC. Otherhardware embodiments are also feasible, such as a circuit built ofseparate logic components. A hybrid of these different implementationsis also feasible. When selecting the method of implementation, a personskilled in the art will consider the requirements set for the size andpower consumption of the apparatus, the necessary processing capacity,production costs, and production volumes, for example.

In an embodiment, an apparatus comprises means for obtaining positionand timing information from a satellite positioning system; means fortuning to a frequency channel with GSM transmission; means forcollecting a group of in phase and quadrature samples for the length of12 GSM frames; means for performing peak detection using at least twopeak detectors over the group of samples wherein the found peak valuesare the locations of synchronization bursts SCH; means for, determiningthe timing information, carrier-to-noise ratio, in phase and quadraturevalues for the found peaks; means for collecting a group of in phase andquadrature samples for the length of 12 or 51 GSM frames; means fordetermining from the found SCH base station identification code BSIC,frame number and BCCH training sequence for all SCH; means for decodingBCCHs corresponding to all SCH; and means for determiningtime-difference-of-arrival between the found peak values using thedetermined timing information.

It will be obvious to a person skilled in the art that, as technologyadvances, the inventive concept can be implemented in various ways. Theinvention and its embodiments are not limited to the examples describedabove but may vary within the scope of the claim.

The invention claimed is:
 1. An apparatus comprising at least oneprocessor configured to cause the apparatus to: control a satellitepositioning system receiver to obtain position and timing informationfrom a satellite positioning system; control a receiver to tune to afrequency channel with Global System for Mobile communication (GSM)transmission; control a receiver to collect a group of in phase andquadrature (I/Q) samples for the length of 12 GSM frames; performcorrelation on the group of I and Q samples; perform peak detectionusing at least two peak detectors over the group of samples wherein thefound peak values are the locations of synchronization bursts (SCH); forthe found peaks, determine the timing information, carrier-to-noiseratio, in phase and quadrature values; control a receiver to collect agroup of in phase and quadrature (I/Q) samples for the length of 12 or51 GSM frames; from the found SCH, determine base station identificationcode BSIC, frame number and Broadcast Control Channel (BCCH) trainingsequence for all SCH; decode BCCHs corresponding to all SCH; anddetermine time-difference-of-arrival (TDOA) between the found peakvalues using the determined timing information.
 2. The apparatus ofclaim 1, wherein the at least one processor further configured todetermine timing information of the found peaks utilizing informationobtained from the satellite positioning system.
 3. The apparatus ofclaim 2, the apparatus being configured to determine timing informationof found peaks, the information comprising sample index relative to thestart of collecting and sample index relative to satellite positioningsystem timing information.
 4. The apparatus of claim 1, the apparatusbeing configured to determine cell identification and cell siteinformation from BCCHs corresponding to all SCH.
 5. The apparatus ofclaim 1, the apparatus being configured to determine carrier-to-noiseratios and in phase and quadrature values for samples corresponding tothe peak value and one sample early and one sample later the peak value.6. The apparatus of claim 5, the apparatus being configured to utilizethe carrier-to-noise ratio information determined from samplescorresponding to the peak value and one sample early and one samplelater the peak value in determining timing information of found peaks.7. The apparatus of claim 1, the apparatus being configured to determineaverage phase angle error value for synchronization bursts utilizing thein phase and quadrature value information determined from samplescorresponding to the peak value and one sample early and one samplelater the peak value.
 8. The apparatus of claim 1, the apparatus beingconfigured to associate decoded SCH and BCCH bursts with the receivedsignals to identify interfering cells.
 9. The apparatus of claim 1,wherein the correlation is implemented in a field-programmable gatearray (FPGA).
 10. A method for recognizing Global System for Mobilecommunication (GSM) signals, the method comprising: obtaining positionand timing information from a satellite positioning system; tuning to afrequency channel with Global System for Mobile communication (GSM)transmission; collecting a group of in phase and quadrature (I/O)samples for the length of 12 GSM frames; performing correlation on thegroup of I and Q samples; performing peak detection using at least twopeak detectors over the group of samples wherein the found peak valuesare the locations of synchronization bursts (SCH); for the found peaks,determining the timing information, carrier-to-noise ratio, in phase andquadrature values; collecting a group of in phase and quadrature (I/Q)samples for the length of 12 or 51 GSM frames; from the found SCH,determining base station identification code BSIC, frame number andBroadcast Control Channel (BCCH) training sequence for all SCH; decodingBCCHs corresponding to all SCH; and determiningtime-difference-of-arrival (TDOA) between the found peak values usingthe determined timing information.
 11. The method of claim 10, furthercomprising: determining timing information of the found peaks utilizinginformation obtained from the satellite positioning system.
 12. Themethod of claim 11, further comprising: determining timing informationof found peaks, the information comprising sample index relative to thestart of collecting and sample index relative to satellite positioningsystem timing information.
 13. The method of claim 10, furthercomprising: determining carrier-to-noise ratios and in phase andquadrature values for samples corresponding to the peak value and onesample early and one sample later the peak value.
 14. The method ofclaim 13, further comprising: utilizing the carrier-to-noise ratioinformation determined from samples corresponding to the peak value andone sample early and one sample later the peak value in determiningtiming information of found peaks.
 15. The method of claim 10, furthercomprising: determining cell identification and cell site informationfrom BCCHs corresponding to all SCH.
 16. The method of claim 10, furthercomprising: determining average phase angle error value forsynchronization bursts utilizing the in phase and quadrature valueinformation determined from samples corresponding to the peak value andone sample early and one sample later the peak value.
 17. The method ofclaim 10, further comprising: associating decoded SCH and BCCH burstswith the received signals to identify interfering cells.
 18. A computerprogram product embodied on a distribution medium readable by a computerand comprising program instructions which, when loaded into anapparatus, execute a computer process comprising: controlling asatellite positioning system receiver to obtain position and timinginformation from a satellite positioning system; controlling a receiverto tune to a frequency channel with Global System for Mobilecommunication (GSM) transmission; controlling a receiver to collect agroup of in phase and quadrature (I/O) samples for the length of 12 GSMframes; performing correlation on the group of I and Q samples;performing peak detection using at least two peak detectors over thegroup of samples wherein the found peak values are the locations ofsynchronization bursts (SCH); for the found peaks, determining thetiming information, carrier-to-noise ratio, in phase and quadraturevalues; controlling a receiver to collect a group of in phase andquadrature (I/Q) samples for the length of 12 or 51 GSM frames; from thefound SCH, determining base station identification code BSIC, framenumber and Broadcast Control Channel (BCCH) training sequence for allSCH; decoding BCCHs corresponding to all SCH; and determiningtime-difference-of-arrival (TDOA) between the found peak values usingthe determined timing information.